1. Field of the Invention
The present invention relates to air driven power generators, particularly to power generation, size, weight, and efficiency improvements of ram-air driven turbines, and, more particularly, to a system and method that develop an aerodynamic low-pressure region at the discharge side of an air-driven turbine has been developed. The invention generates an increased ratio of total-to-static pressure across a Ram Air Turbine (RAT) developed for a combined ram air Prime Power Generating unit (PPG), resulting in increased turbine power generation when compared to a RAT without the invention. Improvements in the ram-air turbine design and the functionality of the turbine exhaust ducting provide increased power extraction capability resulting in a smaller and lighter power generator that minimizes the overall system size and weight.
2. Description of the Related Art
A RAT is a turbine driven by free-stream air that flows past an aircraft during flight. RATs can be used to develop mechanical power, which, if desired, can be directly converted into electrical power using a generator. The mechanical shaft power can also be used to power any mechanical device, including but not limited to hydraulic systems, vapor-compression cooling system compressors, circulation pumps, or refueling pumps. Electrical power can be used for electronic systems, such as onboard avionics equipment, electronic warfare equipment, and auxiliary backup power systems. RATs can be mounted directly onboard an aircraft fuselage or on secondary wing mounted pods or stores. At wing-mounted locations, the RAT can be located either at an external location where the turbine is directly exposed to free-stream air, or an internal location inside a pod, where the free-stream air is ducted to the turbine through an air inlet that is exposed to free-stream air. Prior work on internal RAT's have utilized ducts to deliver free-stream air to the turbine, by locating the RAT internally, pressure losses occur in the inlet ducting, which decreases turbine output power. They are also limited to ambient static pressure on the turbine discharge. The new invention makes it more feasible to locate a RAT in an interior location and extract additional power relative to a traditional internally mounted RAT.
U.S. Pat. No. 3,463,402 teaches the use of an ejecting exhaust nozzle to generate turbulence between two streams of gas, thus suppressing the noise normally generated from shear stresses at the interface of the higher velocity core gas stream with the lower velocity gas stream in a gas turbine engine.
U.S. Pat. No. 3,409,228 teaches an ejector nozzle for cooling a gas turbine engine and exhaust nozzle, whereby an ejector is in flow communication with an engine inlet and its purpose is to draw additional ram airflow through a bypass duct to provide cooling to the engine and exhaust nozzle.
U.S. Pat. No. 5,435,127 also teaches the use of an ejector nozzle to provide cooling airflow to components of a gas turbine engine; however, this system requires an additional boost pump.
U.S. Patent Application Publication No. 2009/0263244 A1 teaches the use of a mixer/ejector device that improves the performance of a water turbine through mixing of the turbine discharge and a secondary flow stream, increasing the turbine mass flow rate and overall energy extraction. This device is described as applying to ocean-, tidal-, and river/stream-currents.
U.S. Pat. No. 6,804,948 teaches the use of a lobe mixer for a jet engine that efficiently mixes two streams of gases by contouring of the lobes to reduce the noise normally generated while suppressing thrust losses caused by mixing.
U.S. Pat. No. 4,819,425 teaches the use of a lobe mixer with vent openings located within the lobe surfaces for noise suppression in a high bypass turbofan jet engine.
U.S. Patent Application Publication Nos. 2008/0105487 A1 and 2008/0105488 A1 both teach a curved lobe mixer for a bypass turbomachine comprising circumferentially distributed lobes that mix concentric gas streams within a converging-diverging flow nozzle to achieve noise suppression.
U.S. Pat. No. 4,149,375 teaches the use of a lobe mixer device with “scalloped” side walls that provide efficient mixing of two flow streams for improved noise suppression and/or engine performance with minimal pressure losses.
Above-referenced co-pending U.S. patent application Ser. No. 12/333,770 teaches the uses of converging/diverging ram air ejector nozzles to improve the performance of a RAT; however, this unit does not specifically address mixing techniques between the flow in the converging/diverging ram air ejector and the turbine exhaust, and mixing between the combined converging/diverging flow and the free-stream air surrounding the unit.
None of the cited prior art teaches the use of a converging/diverging ram air ejector nozzles with the use of a lobe mixer devices to enhance mixing between multiple flow streams to augment the total-to-static pressure ratio across a ram air driven turbine for the purpose of increasing power.
The mechanical power that can be developed from a RAT is a function of the specific work of the fluid, which is the total-to-static pressure ratio across the turbine rotor divided by the density of the fluid. The pressure at the face of the turbine rotor is a function of the aircraft velocity, altitude, inlet pressure drop, and environmental conditions and is specified as the total pressure or the maximum obtainable pressure that can be utilized for power generation. If a method to decrease the static pressure is not utilized, the power generating capability of the RAT is limited to the total pressure developed by the aircraft and the ambient or free-stream static pressure.